This invention relates to stable urea-formaldehyde concentrates containing urea and formaldehyde in a mol ratio of 4.0 to 6.5 mols formaldehyde for every mol of urea, and to a process for their production.
The reaction of formaldehyde and urea in alkaline solution followed by evaporation of water to yield concentrated solutions is well known. U.S. Pat. No. 2,652,377 discloses a urea-formaldehyde concentrate product which has met with considerable commercial success. This type of product is sold mainly for making adhesives for plywood or particle board and for making fertilizers containing water-insoluble, slow-release nitrogen. For use in wood adhesives, the concentrate is mixed with sufficient urea to give a formaldehyde to urea mol ratio of about 1.5, an acid catalyst is added, and the mixture is sprayed or rolled onto the wood which is then heated in a press to cure the resin. To prepare slow-release nitrogen fertilizers, the concentrate is mixed with sufficient urea to adjust the formaldehyde to urea mol ratio to about 0.5, an acid catalyst is added, and the mixture is allowed to react to form a ureaform fertilizer, usually with agitation and in the presence of solid fertilizer ingredients such as ammoniated superphosphate, potassium chloride and dolomite. It has been the practice of the industry to supply both of these uses with the same urea-formaldehyde concentrate; however, each type of application has from time to time experienced considerable difficulty with the product. Processing problems involving sticking of the product and plugging of processing equipment have been particularly troublesome in the use of the concentrate in the fertilizer industry. Short pot life has been the major problem in the adhesive industry. Accordingly, considerable research has been carried out to overcome these problems by providing an optimum urea-formaldehyde concentrate for each of these uses, i.e., one type of product for use in fertilizers and another type of product for use in adhesives.